Chemical-mechanical polishing ("CMP") processes remove material from the surface of semiconductor wafers or other substrates in the production of microelectronic devices and other products. CMP processes typically planarize and/or polish the surface of a substrate in the fabrication of integrated circuits by moving the substrate across a polishing medium.
FIG. 1 is a schematic view that illustrates a conventional CMP machine 10 with a platen 20, a wafer carrier 30, a polishing pad 40, and a planarizing liquid 44 on the polishing pad 40. The platen 20 is typically connected to a drive assembly 26 to rotate the platen 20 (indicated by arrow A) or reciprocate the platen 20 back and forth (indicated by arrow B). Additionally, the wafer carrier 30 generally has a lower surface 32 to which a wafer 12 may be attached, or the wafer 12 may be attached to a resilient pad 34 positioned between the wafer 12 and the lower surface 32. The wafer carrier 30 is generally attached to an actuator assembly 36 to impart axial and/or rotational motion to the wafer 12 (indicated by arrows C and D, respectively), or the wafer carrier 30 may be a weighted, free-floating wafer holder (not shown).
The polishing pad 40 and the planarizing liquid 44 may separately, or in combination, define a polishing medium that mechanically and/or chemically removes material from the surface of a wafer. The polishing pad 40 may be a conventional polishing pad made from a continuous phase matrix material (e.g., polyurethane), or it may be a new generation abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. Conversely, the planarizing liquid 44 may be a conventional CMP slurry with abrasive particles, or it may be a planarizing solution without abrasive particles. In general, abrasive slurries are used with conventional non-abrasive polishing pads and planarizing solutions are used with abrasive polishing pads.
To planarize the wafer 12 with the CMP machine 10, the wafer carrier 30 presses the wafer 12 face-downward against the polishing medium. More specifically, the wafer carrier 30 generally presses the wafer 12 against the planarizing liquid 44 on a planarizing surface 42 of the polishing pad 40, and at least one of the platen 20 or the wafer carrier 30 moves relative to the other to move the wafer 12 across the planarizing surface 42. As the wafer 12 moves across the planarizing surface 42, material is removed from the face of the wafer 12.
In the competitive semiconductor industry, it is desirable to maximize the throughput of finished wafers and to produce a uniform, planar surface on each wafer. The throughput of CMP processing is a function of several factors, one of which is the rate at which the thickness of the wafer decreases as it is being planarized (the "polishing rate"). The polishing rate affects the throughput because the polishing period per wafer decreases with increasing polishing rates and it is easier to accurately endpoint CMP processing with a consistent polishing rate. Thus, it is desirable to have a high, consistent polishing rate.
One manufacturing concern with CMP processing is that the throughput may drop because planarizing wafers alters the condition of the polishing pads. More specifically, particles from the wafer, pad and/or slurry accumulate on the planarizing surface of the polishing pad and form waste matter accumulations that may cover portions of the planarizing surface. The polishing rate accordingly changes during CMP processing, which may make it more difficult to quickly planarize a wafer or endpoint the CMP process. Thus, the waste matter accumulations may reduce the throughput of CMP processing.
CMP processes must also consistently and accurately produce a uniform, planar surface on the wafer because it is important to accurately focus the image of circuit patterns on the surface of the wafer. As the density of integrated circuits increases, it is often necessary to accurately focus the critical dimensions of the circuit pattern to within a tolerance of approximately 0.1 .mu.m. Focusing circuit patterns to such small tolerances, however, is very difficult when the surface of the wafer is not uniformly planar. Thus, planarizing processes must create a highly uniform, planar surface.
Another problem with CMP processing is that the waste matter accumulations reduce the uniformity of the polishing rate across the planarizing surface of a polishing pad. The waste matter accumulations do not accumulate uniformly across the planarizing surface of the polishing pad, and thus the polishing rate may vary unpredictably across the polishing pad. As a result, the surface of a polished wafer may not be uniformly planar.
In light of the problems associated with waste matter accumulations on polishing pads, it is necessary to periodically remove the waste matter accumulations from the planarizing surfaces so that the polishing pads are brought back into a desired state for planarizing substrates ("conditioning"). For example, U.S. Pat. No. 5,456,627 issued to Jackson et al. discloses an apparatus for conditioning a rotating, circular polishing pad with a rotating end effector that has an abrasion disk in contact with a polishing surface of the pad. The end effector described in U.S. Pat. No. 5,456,627 moves along a radius of the polishing pad surface at a variable velocity to compensate for the linear velocity of the polishing pad surface. Additionally, U.S. Pat. No. 5,456,627 discloses maintaining a desired contact force between the end effector and the polishing pad surface with a closed feedback loop in which a load transducer generates a signal with an amplitude proportional to the applied force. A computer then uses the signal from the load transducer to operate an actuator that moves the end effector in a direction so that the output of the load transducer is substantially equal to the desired contact force.
Another conventional conditioning method and apparatus, which is disclosed in U.S. Pat. No. 5,081,051 issued to Mattingly et al., is an elongated blade with a serrated edge that is engaged with a portion of a circular, rotating polishing pad. The blade disclosed in U.S. Pat. No. 5,081,051 is pressed against a polishing path on the planarizing surface of the polishing pad to scrape or cut grooves into the planarizing surface.
Conventional conditioning methods and devices, however, may reduce the pad life of polishing pads because they may over-condition some areas on the planarizing surface. Additionally, conventional conditioning methods and devices may result in a non-planar surface on the polishing pads. Therefore, it would be desirable to develop a method and apparatus that improves the conditioning of polishing pads.